WASHINGTON, March 13 (Reuters) - U.S. President Donald Trump agreed with British Prime Minister Theresa May that Russia must provide "unambiguous answers" about how a Russian-developed chemical agent came to be used against a Russian double agent in Britain, the White House said on Tuesday after the two leaders spoke.

"President Trump agreed with Prime Minister May that the Government of the Russian Federation must provide unambiguous answers regarding how this chemical weapon, developed in Russia, came to be used in the United Kingdom," the White House said in a brief statement on the call. "The two leaders agreed on the need for consequences for those who use these heinous weapons in flagrant violation of international norms." (Reporting by Doina Chiacu Writing by Tim Ahmann Editing by Chris Reese)